A limiting factor on how high of a frequency resonant loads can run is the combined switching losses. There are six main sources of switching losses with bipolar devices (Field Effect Transistor type devices do not have the 3rd and 4th losses listed). They are:                1. The voltage/current (“V/I”) losses at turn on.        2. The V/I losses at turn off.        3. The conduction modulation loses at turn on.        4. The tail current losses at turn off.        5. The diode switching losses.        6. The ½CV2 loss when the switching device is turned on (wherein C is capacitance and V is voltage).        
The V/I losses at turn on are the losses in the switching device when the voltage across the device is falling and the current is rising at the same time. In addition to the V/I losses at turn on, there are the additional losses of a high current (higher than the load current) in the switching device if a diode is being reversed biased (sweep out) at the same time the switch is being turned on.
The V/I losses at turn off are the losses in the switching device when the voltage across the device is rising and the current is falling at the same time.
The conduction modulation losses are the losses in the device just after it is turned on until the forward voltage drop across the device has fallen to its DC forward voltage rating.
The tail current losses take place at the end of the turn off time of a switching device. For most bipolar devices under most switching conditions, a point is reached at which the switching device itself determines the current decay rate and the current decays at a slower rate thereby increasing the power loss. The causes and extent of the tail current losses are complex, but tail current losses are generally due to charges stored in the bipolar devices due to minority carrier injection that occurs when the device is first turned on.
The diode switching losses are typically very high and occur when the diode is reversed biased (sweep out) with current in the diode when the switching device is turned on.
The ½CV2 loss when the switching device is turned on is due to the device absorbing energy stored in the capacitance across the device just before being turned on.